Field of the Disclosure
The present disclosure relates to methods of changing tools mounted on spindles of machine tools, and machine tools for machining a workpiece while changing tools by this tool changing method.
Background of the Disclosure
Conventionally, in a machining center or the like, an optimum tool is selected from a plurality of tools stored in a tool magazine according to the shape of a workpiece as a machining target and the machining method when machining this workpiece, and mounting and detachment of the tool on and from a spindle is automatically performed by an automatic tool changer (an ATC device). As a device automatically mounting and detaching a tool on and from a spindle, a tool changer as disclosed in the Japanese Unexamined Patent Application Publication No. 63-123646 and the like have been suggested.
This conventional tool changer includes a first sleeve rotatably supported on a headstock, a second sleeve which is to be integrally rotated with the first sleeve and is supported to be slidable in its axial direction, a turning arm fixed to a tip of the second sleeve and having tool gripping claws, a rotating shaft driven for rotation by a motor rotatably supported to the headstock, a cam indexer following a first cam actuated based on the rotation of the rotating shaft to cause the first sleeve to rotate, an axis feed following a second cam actuated based on the rotation of the rotating shaft to cause the second sleeve to reciprocate in its axial direction, a tool mounting and detaching device drive similarly following a fourth cam actuated based on the rotation of the rotating shaft to cause a tool mounting and detaching device on a spindle to be driven and cause a tool to be in a clamped/unclamped state, and other components.
According to this tool changer, first, the spindle after one machining is finished is moved to a tool changeable position called an ATC origin position (a tool change position) and the rotation of the spindle is stopped. Also, among tool pots contained in a tool magazine, a tool pot in which the next tool is held is indexed at the tool changeable position. Next, by rotating the drive shaft, the turning arm is turned in a predetermined direction from its original position via the first sleeve and the second sleeve by the cam indexer. Thereby, the second sleeve to which the turning arm is fixed is moved upward by the axis feeder, and the current tool mounted on the spindle and the next tool held in the tool pot are gripped by the tool gripping claws.
Next, by further turning the turning arm in the predetermined direction with the both tools gripped by the tool gripping claws, the tool mounted on the spindle is caused to be in an unclamped state by the tool mounting and detaching device drive. Further, the second sleeve is moved downward by the axis feeder to cause the current tool and the next tool to be pulled out from the spindle and the tool pot, respectively. Thereafter, the turning arm is further turned in the same direction to move the second sleeve upward, that is, move the turning arm upward, and the next tool and the current tool are mounted on the spindle and the tool pot, respectively, and the tool mounted on the spindle is caused to be in a clamped state. Then, the turning arm is turned to release the gripping of the next tool and the current tool by the tool gripping claws, and the turning arm is returned to its original position, thereby ending the series of processes for tool change.
Meanwhile, in the above-described conventional tool changer, to avoid interference with the turning arm, a spindle head including the spindle is stopped at the tool change position during tool change, and the spindle head is moved to a position where machining is started (a machining position) after completion of tool change. However, since the spindle head is moved after completion of tool change, it is impossible to proceed to the next machining until tool change is finished, which causes a standby time until the next machining.
To address this, as a technique for reducing the standby time, a tool changing system has been suggested in which, when it is determined that there is no possibility of interference between the turning arm and the spindle head, the spindle head is moved before the turning arm is returned to its original position, and the rotation of the spindle is started along with the movement of the spindle head (the Japanese Unexamined Patent Application Publication No. 2007-237305).
Thus, starting the movement of the spindle head and the rotation of the spindle before the turning arm is returned to its original position, that is, before tool change is completed makes it possible to reduce the standby time until the next machining.
Meanwhile, in the above-described tool changing system, when the spindle is moved toward the machining position after the next tool is mounted on the spindle, the spindle has to be moved along a tangent direction so as to be away from the turning arm in order to avoid a collision between the spindle and the turning arm.
However, among machine tools, some are configured to move the spindle in a direction along the axis of the spindle when the spindle is moved toward the machining position after the next tool is mounted on the spindle. In a machine tool thus configured, to avoid a collision between the spindle and the turning arm, the movement of the spindle head and the rotation of the spindle cannot be started unless the turning arm has been returned to its original position.
That is, in the above-described tool changing system, it is merely possible to reduce the standby time until the next machining only when the spindle is moved along a tangent direction so as to be away from the turning arm after the next tool is mounted on the spindle. In other cases, a problem of occurrence of the standby time still remains. Further, in the PTL 2, neither specific method nor means for reducing the standby time until the next machining in other cases is disclosed.